Electrode catheter positioning system

ABSTRACT

A system for determining a position of a catheter is provided. An electrode is on a catheter. A plurality of reference electrodes are provided. Each of the plurality of reference electrodes are configured to transmit or receive a signal to or from the electrode, respectively. A processor is operable to determine a position of the catheter as a function of an electrical characteristic based on the signals. The plurality of reference electrodes are not positioned on or in a body surface along three mutually orthogonal axes.

BACKGROUND

The present embodiments relate to medical catheters. In particular,accurate positioning of a catheter inside a body using electrodes isprovided.

Catheters are used for several types of medical procedures. For example,catheters are used to measure electrical activity, capture image data,and/or apply stents within a body. Additionally, catheters are used forablation therapy, especially for the treatment of heart disease. Thepositioning of such catheters during treatment or measurement proceduresis of great interest to medical professionals due to the limited area tonavigate within or due to navigation near sensitive internal organs.

A variety of medical imaging systems are used to assist medicalprofessionals with maneuvering and positioning catheters within a body.For example, ultrasound, computed tomography (“CT”), and X-ray systemsare used to generate images of the catheter within the body duringtreatment or measurement procedures. However, minimizing the use ofimaging systems during the catheter procedures may be desired to reducecost as well as minimize exposure, such a X-rays, to the patient.

Catheter positioning systems may not utilize external medical imagingsystems during the entire treatment or measurement procedures.Specialized catheters having coils or transducers or systems utilizingpatches positioned along three mutually orthogonal axes on a bodysurface have been proposed. However, the use of such systems mayincrease cost as well as complexity.

BRIEF SUMMARY

By way of introduction, the preferred embodiments described belowinclude catheters including electrodes, body surface electrodes, andmethods of positioning a catheter within a body. A plurality ofreference electrodes are provided. A catheter having an electrode isoperable to communicate with the reference electrodes, and a position ofthe catheter is determined based on the communication between theelectrodes.

According to a first aspect, a system for determining a position of acatheter is provided. An electrode is on a catheter. A plurality ofreference electrodes are provided. Each of the plurality of referenceelectrodes are configured to transmit or receive a signal to or from theelectrode, respectively. A processor is operable to determine a positionof the catheter as a function of an electrical characteristic based onthe signals. The plurality of reference electrodes are not positioned onor in a body surface along three mutually orthogonal axes.

According to a second aspect, a system for determining a position of acatheter is provided. First and second electrodes are on a catheter. Aplurality of reference electrodes are provided. Each of the plurality ofreference electrodes are configured to transmit or receive a signal toor from the first and second electrodes, respectively. A processor isoperable to determine a position of the catheter as a function of avoltage potential between the second electrode and one of the pluralityof reference electrodes when the first electrode and another one of theplurality of reference electrodes are transmitting and receiving thesignal, respectively.

According to a third aspect, a method for determining a position of acatheter is provided. A catheter is inserted in a body. The catheter hasa first electrode. A first reference catheter is inserted in the body.The first reference catheter has a first set of a plurality of referenceelectrodes. A signal is generated between one of the plurality ofreference electrodes and the first electrode. An electricalcharacteristic is determined based on the signal. A position of thecatheter is determined using the electrical characteristic.

The present invention is defined by the following claims, and nothing inthis section should be taken as a limitation on those claims. Furtheraspects and advantages of the invention are discussed below inconjunction with the preferred embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

The components and the figures are not necessarily to scale, emphasisinstead being placed upon illustrating the principles of the invention.Moreover, in the figures, like reference numerals designatecorresponding parts throughout the different views.

FIG. 1 is a general diagram illustrating one embodiment of a system fordetermining a position of a catheter;

FIG. 2 is a magnified view of one embodiment of the system fordetermining a position of a catheter of FIG. 1;

FIG. 3 is a magnified view of a first alternate embodiment of the systemfor determining a position of a catheter of FIG. 1;

FIG. 4 is a magnified view of a second alternate embodiment of thesystem for determining a position of a catheter of FIG. 1;

FIG. 5 is a magnified view of a third alternate embodiment of the systemfor determining a position of a catheter of FIG. 1; and

FIG. 6 is a flowchart illustrating one embodiment of a method fordetermining a position of a catheter.

DETAILED DESCRIPTION OF THE DRAWINGS AND PRESENTLY PREFERRED EMBODIMENTS

A position of a treatment and/or measurement catheter having electrodescan be determined in a two step approach. Firstly, relative distancesbetween reference body surface electrodes or electrodes on a referencecatheter and the electrodes on the treatment and/or measurement catheterare calibrated by image segmentation using X-ray images. Secondly,distances between the treatment and/or measurement catheter and thereference catheter or reference body surface electrodes are measured byestimating the impedance of blood between the electrodes or measuringthe voltage potential between non-transmitting or non-receivingelectrodes. Several reference catheters and/or reference body surfaceelectrodes can be used to obtain more accurate positioning information.The accurate position of electrodes in the measurement and/or treatmentcatheter is measured either in a sequential manner or using signals withdifferent frequencies, and the accurate position is derived usingtriangulation methods. Also, heart beat motion and breathing motion canbe compensated for by various triggering techniques. Coordinate positiondata gathered by the system may be used in conjunction with an imagevolume data set to enable a three dimensional (“3D”) animation of themeasurement and/or treatment catheter within a body.

FIG. 1 is a general diagram illustrating one embodiment of a system fordetermining a position of a catheter 124. The system includes, but isnot limited to an imaging system 100, an electrode system 120, acatheter 124, reference catheters 128, and reference body surfaceelectrodes 130. Fewer or more components may be utilized.

The imaging system 100 is a X-ray system, CT system, ultrasound system,or any known or future medical imaging system. For example, the imagingsystem 100 is a X-ray system operable to generate X-ray images of achest region of a patient 112. The imaging system 100 includes aprocessor 102, a memory 106, a display 110, and/or any known or futureelectronic and/or audio/visual hardware used for medical imaging.

The processor 102 is in communication with the memory 106 and thedisplay 110. The processor 102 is a main processor, such as amicroprocessor, or a plurality of processors operable to communicatewith electronics of the imaging system 100. The memory 106 is any knownor future storage device. For example, the memory 106 is a non-volatileand/or volatile memory, such as a Random Access Memory “RAM”(electronic), a Read-Only Memory “ROM” (electronic), or an ErasableProgrammable Read-Only Memory (EPROM or Flash memory). The display 110is any mechanical and/or electronic display positioned for accessibleviewing by a doctor or medical professional. For example, the display110 is a liquid crystal display, (“LCD”), printer, or cathode ray tube(“CRT”) monitor. The display 110 is operable to show 2D, 3D, and/or fourdimensional (“4D”) images (i.e., the fourth dimension is time, and,therefore, 4D images are a sequence of images that show an object over atime period).

The imaging system 100 is operable to process or run any variety ofknown of future medical imaging software protocols and/or applications.For example, the imaging system 100 includes or is operable to loadprograms or applications for determining calibration position data forthe catheter 124 within the patient 112 as well as for processing imagedata and rendering 2D, 3D, and/or 4D images.

The electrode system 120 is in communication with the imaging system100. The electrode system 120 includes, but is not limited to, aprocessor 130 and a memory 140. The processor 130 is in communicationwith the processor 130. The processor 130 is a main processor, such as amicroprocessor, or a plurality of processors operable to communicatewith electronics of the electrode system 120. The memory 140 is anyknown or future storage device. For example, the memory 140 is anon-volatile and/or volatile memory, such as a Random Access Memory“RAM” (electronic), a Read-Only Memory “ROM” (electronic), or anErasable Programmable Read-Only Memory (EPROM or Flash memory).

The electrode system 120 is operable to receive calibration data fromthe imaging system 100 and to process electrical signals from thecatheter 124, the reference catheters 128, and/or the body surfaceelectrodes 130 to determine an internal position of the catheter 124.Additionally, the electrode system 120 may transmit the catheter 124position data to the imaging system 100 to display a 3D animation orvirtual image of the catheter inside the patient 112.

Alternatively, the imaging system 100 and the electrode system 120 areone system. Or, the imaging system 100 and the electrode system 120 areseparate systems that are not in communication with each other. In thiscase, calibration data acquired by the imaging system 100 is transferredor entered into the electrode system 120, and position data of thecatheter 124 determined by the electrode system 120 is used to displayan image of the catheter 124 on a display connected with the electrodesystem 120, the imaging system 100, or another imaging system. Anycombination of features and components of the imaging system 100 and theelectrode system 120 may combined or separated in one or more systems.

The patient 112 is any living or nonliving object. For example, thepatient 112 is an animal or human being. The catheter 124 and thecatheters 128 are inserted through any part or region of the patient 112to be positioned in or by any anatomical feature for treatment and/ormeasurement purposes. For example, to measure heart activity or toperform ablation therapy on the heart of the patient 112, the catheter124 and the reference catheters 128 are inserted into a limb, such as anarm or leg, of the patient 112 to enter into a vein or artery that leadsto the heart. For example, the catheter 124 is inserted into a femoralvein of the patient 120. The reference catheters 128 may be insertedinto the same vein or other veins. Alternatively, the catheter 124 andthe reference catheters 128 are inserted in the throat, chest, abdomen,any opening or orifice, or any other part of the patient 112. The bodysurface electrodes 130 may be attached to any part of the patient 112'sbody in conjunction with the catheter 124 and the reference catheters128. For example, the body surface electrodes 130 are attached on thechest of the patient 112. The body surface electrodes 130 may bepositioned at specific locations, such as at a particular distance anddirection from the naval and/or nipples.

Referring to FIG. 2, the catheter 124 is a treatment catheter used forablation therapy or applying stents, a measurement catheter used formeasuring electrical or other physiological activity, an imagingcatheter, such as an ultrasonic catheter, and/or any other known orfuture catheter. For example, the catheter 124 includes a body or lumenhaving a longitudinal axis and a circumference. The body or lumen is aflexible shaft that is made of a plastic, a polymer, and/or any known orfuture flexible material. The lumen is sized for insertion into thecirculatory system, such as less than about 5 mm in diameter. The bodymay include a flexible tip and/or guide wires. Also, the catheter 124may include a handle and/or a steering mechanism.

Pairs of electrodes 201 are disposed on or in the body of the catheter124. Alternatively, the electrodes 201 may be disposed in non-pairconfigurations. The electrodes 201 are disposed spaced apart from thedistal end of the catheter 124 to any predetermined position along thelength of the body of the catheter 124. The electrodes 201 form acontinuous or non-continuous loop around the body of the catheter 124allowing contact with blood or tissue within the patient 112.Alternatively, predetermined grooves may be set in the outer surface ofthe catheter 124 to receive the electrodes 201 so that the electrodes201 are flush with the rest of the outer surface of the catheter 124.The electrodes 201 are made of any metal material or any known or futurematerial operable to transmit and receive electrical signals.Alternatively, the electrodes 201 are made of a non-magnetic materialthat may be scanned with a magnetic resonance imaging (“MRI”) system andyet still transmit and receive electrical signals. The electrodes 201are connected with the electrode system 120. The electrodes 201 are alsoconnected with a voltage or current generator, which may or may not bepart of the electrode system 120. The generator is connected with all orsome of the electrodes 201. For example, the generator is connected toone electrode 201 in each pair of the electrodes 201. The generator maybe connected to one electrode 201 in the most distal pair, the mostproximal pair, and a middle pair of electrodes 201.

The reference catheter 128 is a catheter for transmitting and receivingelectrical signals. For example, the reference catheter 128 includes abody or lumen having a longitudinal axis and a circumference. The bodyor lumen is a flexible shaft that is made of a plastic, a polymer,and/or any known or future flexible material. For example, the body ofthe reference catheter 128 has a curvilinear shape. Also, the referencecatheter 128 may include a handle and/or a steering mechanism.

Electrodes 205 are disposed on the body of the reference catheter 128.The arrangement and type of the electrodes 205 are similar to or thesame as the electrodes 201, as described above. Different arrangementsand/or type may be used. The electrodes 205 are not positioned on or inthe body surface of the patient 112 along three mutually orthogonalaxes. The electrodes 205 are connected with the electrode system 120.The electrodes 205 are also connected with a voltage or currentgenerator, which may or may not be part of the electrode system 120. Thevoltage or current generator may be the same generator used inconjunction with the catheter 124 or may be a separate generator. Therespective generator is connected with all or some of the electrodes205.

For example, the voltage or current generator for the catheter 124generates an alternating current (“AC”) signal, such as a low currentsignal at about 10 kHz, and transmits the signal from one electrode 201,and the voltage or current generator for the reference catheter 128generates a signal at substantially the same frequency with a phaseshift of 180 degrees and transmits that signal from one electrode 205.By having a 180 degree phase shift, a current is created between theelectrode 201 and the electrode 205. To insure that the current isfloating from the electrode 201 and the electrode 205, these electrodesare controlled to have low impedance in relation to the otherelectrodes. This is accomplished by phase shifting two generatorsconnected to the electrode 201 and the electrode 205, respectively. Thephase shifting acts as a current pump where electrons are pumped fromone electrode to another electrode. A current may be generated betweenany of the electrodes 201 and 205, respectively. This transmitting andreceiving configuration between the electrodes 201 and 205 is timedivided so that one frequency is used. Alternatively, the same voltageor signal generator is used for both the electrodes 201 and 205. Or,separate voltage or current generators are used for each or a group ofelectrodes 201 and 205 to allow for the use of different frequencieswithout sequentially transmitting or receiving signals between theelectrodes 201 and 205.

Also, a direct current (“DC”) signal may be used between the electrodes201 and 205. For example, DC generators connected with the catheter 124and the reference catheter 128 may allocate specific sinking andsourcing timing configurations to allow for a DC current between acertain electrode 201 and a certain electrode 205.

A position of an electrode 201 is determined based on an electricalcharacteristic of the signal between the electrode 201 and a respectiveelectrode 205. For example, an impedance of blood between the electrode201 and the electrode 205 is calculated using any known or futuremathematics or physics calculation or equation, such as Ohms' law. Thedifferent impedances between electrodes relate to the distances betweenthe same electrodes. For example, the impedance will increase as thedistance between electrodes increases. A predetermined look-up table maybe used to store distance values that correlate to different impedances.These values may be obtained by testing the patient 112 or otherpatients. Alternatively, the values may be obtained by testing randomblood samples. The distances r1, r2, and r3 are determined based on therespective impedance using a transfer function or any other mathematicaltechnique in conjunction with the look-up table. Because the relativepositions of the electrodes 205 on the reference catheter 128 and theelectrodes 201 on the catheter 124 are known, the distances d1 and d2 aswell as the angles α1, α2, α3, β1, β2, and β3 can be determined. Therelative distances and angles may be used in triangulation formulas,trigonometric equations, and/or any other known or future mathematicaltechniques to derive a three point coordinate position of the electrode201. Ultimately, the position of the catheter 124 is determined becausethe placement of the electrodes 201 on the catheter 124 is known.Positions may be determined for any number of electrodes 201 as well asany number of different catheters.

Alternatively, instead of calculating blood impedance, a voltagepotential between a certain electrode 205 and a certain electrode 201may be measured to determine the distance between the electrodes. Forexample, when one electrode 205 is transmitting or receiving a signalfrom one electrode 201., an electric field is generated due to thecurrent flow. Therefore, a voltage potential, created by the electricfield, may be measured between another electrode 205, such as anelectrode adjacent to the transmitting or receiving electrode 205, andanother electrode 201, such as an electrode adjacent to the transmittingor receiving electrode 201. The different voltage potentials betweenelectrodes relate to the distances between the same electrodes. Forexample, the voltage measured will increase as the distance betweenelectrodes increases. A predetermined look-up table may be used to storedistance values that correlate to different voltage potentials. Thesevalues may be obtained by testing the patient 112 or other patients.Alternatively, the values may be obtained by testing random bloodsamples. The distances r1, r2, and r3 are determined based on therespective voltage potential using a transfer function or any othermathematical technique in conjunction with the look-up table. Thedistances d1 and d2 as well as the angles α1, α2, α3, β1, β2, and β3 canbe determined by any technique described above.

The electrodes 201 and 205 are unlike magnetic coils that create anelectromagnetic field to induce electric currents in adjacent coils. Theamplitude of the electric current is proportional to the distance fromthe coil generating the field. Hence, the amplitude of the inducedcurrent is a measure of the distance. The angle of the coil in relationto the magnetic field is also of importance. When three perpendicularcoils are positioned at the tip of a catheter, three electrical currentscan be measured in which the geometric relation also gives informationof catheter direction. However, using electrodes does not involvegenerating electromagnetic fields to induce electric currents inadjacent coils. An electric current is sent from one electrode toanother to create a potential field through the blood pool and/or tissuebetween the electrodes where a continuous potential drop is created. Theelectric current is generated using phase shifting as described above.For example, the current is about 0.1 mA at 10 kHz. In this way,impedance and/or voltage potential relating to distance may bedetermined. Also, the electric current is continuously moving orchanging as the catheter 124 is moving.

Also, the magnetic coil approach includes coils generating the fieldthat need to be positioned at a known position either inside or outsidethe patient 112 as well as measurement coils that need to be integratedin the catheter. Therefore, specific catheters are used, unlike theelectrode approach in which catheters with simple electrodes may beused. The position is determined without using electrodes external tothe patient, but such electrodes may be used.

FIG. 3 is a magnified view of a first alternate embodiment of the systemfor determining a position of the catheter 124. In this embodiment, tworeference catheters 128 are used. However, any number of referencecatheters 128 may be used. More reference catheters 128 allow for moreaccurate position data. The reference catheters 128 can be positioned inany direction in the patient 112. For example, the reference catheters128 are positioned at an angle to each other. Therefore, the referencecatheters 128 may be substantially straight. Alternatively, thereference catheters 128 are curvilinear in shape.

The reference catheters 128 share the same voltage or current generatoror they each utilize a separate generator. As mentioned above, aposition of the electrode 124 is determined based the signalstransmitted and received between the electrodes 201 and 205,respectively. Relative distances between the electrodes 201 and 205 aredetermined by blood impedance, voltage potential, and/or any otherelectrical characteristic. The distances r1, r2, r3, r4, d1 and d2 aswell as the angles α1, α2, α3, β1, β2, and β3 can be determined by anytechnique described above.

FIG. 4 is a magnified view of a second alternate embodiment of thesystem for determining a position of the catheter 124. In this case, thebody surface electrodes 130 are used as reference electrodes instead ofthe reference catheter 128. The body surface electrodes 130 are placedon any part of the patient 112's body. For example, the body surfaceelectrodes 130 are not positioned on or in the body surface along threemutually orthogonal axes. Instead, the electrodes 130 may be positionedbased on body location or more random locations on the patient. The bodysurface electrodes 130 are made of any metal material or any known orfuture material operable to transmit and receive electrical signals. Forexample, the body surface electrodes 130 are electrocardiogram (“ECG”)electrodes. Alternatively, the body surface electrodes 130 are made of anon-magnetic material that may be scanned with a magnetic resonanceimaging (“MRI”) system and yet still transmit and receive electricalsignals. For example, titanium or carbon fiber material may be used.Also, the body surface electrodes 130 may be needle or pin electrodesthat can be inserted in the body surface of the patient 112. The bodysurface electrodes 130 are connected with the electrode system 120 or aseparate or included ECG system. The electrodes 201 are also connectedwith a voltage or current generator, which may or may not be part of theelectrode system 120 or the ECG system. The generator is connected withall or some of the electrodes 130.

The operation of the body surface electrodes 130 and the electrodes 201configuration is substantially similar to the reference catheter 128 andthe catheter 124 configuration, as described above. The position of theelectrode 201 is determined based on the signals transmitted andreceived between the electrodes 201 and 130, respectively. Relativedistances between the electrodes 201 and 130 are determined byimpedance, voltage potential, and/or any other electricalcharacteristic. In this case, in addition to blood impedance, animpedance of other tissue, such as lung tissue as well as other thoracicimpedance, is determined. A predetermined look-up table may be used tostore distance values that correlate to combinations of differentimpedances. These values may be obtained by testing the patient 112 orother patients. Alternatively, the values may be obtained by testingrandom blood and other tissue samples. The distances r1, r2, r3, d1 andd2 as well as the angles α1, α2, α3, β1, β2, and β3 can be determined byany technique described above.

The impedance between the catheter electrodes and the body surfaceelectrodes may vary due to motion when the patient 112 is breathing,inflation of air in the lungs, and possibly varying contact impedance ofeach of the body surface electrodes. To compensate for this, breathingactivity may be measured and used in a feed forward compensation.Alternatively, filters to remove the low frequency disturbing variationmay be utilized.

Any number and combinations of the body surface electrodes 130 and thereference catheters 128 may be utilized to determine the position of thecatheter 124. For example, referring to FIG. 5, one reference catheter128 is used in conjunction with two body surface electrodes 130 todetermine the position of the catheter 124. However, any number ofreference catheters 128 and body surface electrodes 130 may be used. Forexample, at least two reference catheters 128 and at least six bodysurface electrodes 130 are utilized. More reference catheters 128 andbody surface electrodes 130 that are used allow for more accurateposition data.

The reference catheter 128 and the body surface electrodes 130 share thesame voltage or current generator or they each utilize a separategenerator. As mentioned above, a position of the electrode 124 isdetermined based on the signals transmitted and received between theelectrodes 201, 205, and 130, respectively. Relative distances betweenthe electrodes 201, 205, and 130 are determined by impedance, such asthoracic and blood impedance, voltage potential, and/or any otherelectrical characteristic. The distances r1, r2, r3, r4, d1 and d2 aswell as the angles α1, α2, α3, β1, β2, and β3 can be determined by anytechnique described above.

In any of the embodiments described above, more accurate position datais obtained, especially for non-homogenous blood and other tissuecharacteristics between different patients 112 or in the same patient112, by calibrating the catheter 124 with the reference catheters 128and/or the body surface electrodes 130. Calibration involves generatingimages, such as X-ray image segmentations, while transmitting andreceiving electrical signals between the electrodes 205, 130, and 201.The X-ray images are taken when the catheter 124 is positioned indifferent locations and the reference catheters 128 and/or the bodysurface electrodes 130 remain in the same position. A correlationbetween the actual distances between electrodes determined by the imagesand the distances estimated by the electrode system 120 may be obtained.The correlations are stored in the memory 140 and/or 106 and are reliedon to obtain accurate position data of the catheter 124 during medicalprocedures. The correlations may be used in conjunction with thepredetermined look up tables, described above, to adjust the distancevalues appropriately. For example, an adjusted offset based on acorrelation is added to an output of a predetermined look up table.

Heart beat and breathing patterns can be compensated for by using avariety of techniques. For example, position data may be determined onceduring every heart beat or breathing cycle by triggering the electrodesystem 120 with the respective physiological cycle. Any other known orfuture physiological compensation technique may be utilized.

FIG. 6 is a flowchart illustrating one embodiment of a method fordetermining a position of the catheter 124. In act 601, a catheter isinserted in a body, such as the body of the patient 112. The catheter isany treatment or measurement catheter, such as the catheter 124,including electrodes on the body of the catheter. Any known or futuremethods of inserting the catheter may be utilized. For example, anincision is made in the patient 112, such as in the arm or the leg, andthe catheter 124 is inserted into the incision by a doctor, medicalprofessional, and/or machine. Alternatively, a needle or puncturingdevice may be inserted into the patient 112, and the catheter 124follows the puncturing device. Or, the catheter 124 is inserted into anyorifice or opening of the patient 112. Any known or future lubricant ormechanical, electrical, and/or catheter guide may be used in assistingwith inserting the catheter 124 into the patient 112.

In act 605, a first reference catheter is inserted in the body. Thefirst reference catheter is any catheter including a first set of aplurality of reference electrodes, such as the reference catheter 128.Any of the methods of inserting a catheter in a body described above maybe utilized to insert the first reference catheter. Alternatively, bodysurface electrodes, such as the electrodes 130, are attached on the bodysurface of the patient 130 instead of inserting the first referencecatheter. For example, the electrodes 130 are not positioned on or inthe body surface of the patient 112 along three mutually orthogonalaxes.

In act 609, a second reference catheter is inserted in the body. Thesecond reference catheter is any catheter including a second set of theplurality of reference electrodes, such as another reference catheter128. Any of the methods of inserting a catheter in a body describedabove may be utilized to insert the second reference catheter.Alternatively, body surface electrodes, such as the electrodes 130, areattached on the body surface of the patient 130 instead of inserting thesecond reference catheter. For example, the electrodes 130 are notpositioned on or in the body surface of the patient 112 along threemutually orthogonal axes.

In act 613, a calibration procedure is performed. For example, once thefirst reference catheter, the second reference catheter, and/or the bodysurface electrodes are positioned in or on the patient 112, they remainat their respective positions. The catheter 124 is then moved to oneregion within the body, and the electrodes 201 and the electrodes 205and/or 130 transmit and receive electrical signals between each other,respectively.

Voltage or current generators connected with the electrodes generate acurrent between two specific electrodes. For example, a generator isconnected with the electrodes 201 and one or more generators areconnected with the reference electrodes 205 and/or 130. The generatorsmay be connected with all or some of the respective electrodes. Thegenerators are phase shifted 180 degrees to allow for a path of leastresistance between any two electrodes. The electrical signals betweenthe electrodes may be AC or DC signals. When using AC signals,sequential transmission of the signals between electrodes is performedto allow for the use of a substantially same frequency. Alternatively,more generators may be used to transmit and receive electrical signalsbetween electrodes at different frequencies.

While electrical signals are being generated between the electrodes whenthe catheter 124 is in the first position, images, such as X-ray images,are taken. The actual distances between the electrodes 201 and thereference electrodes 205 and/or 130 are determined from the images, andthe distances are correlated with estimated distance values. Theestimated distance values directly relate to impedance values or voltagepotential values determined based on the electrical signals. Forexample, a medical professional obtains actual distance data from theimages and compares the actual distance data with the estimated distancedata determined by the electrode system 120. Compensation values basedon the comparison are manually entered into the electrode system 120 forcalibration purposes. Alternatively, the imaging system 100 determinesthe actual distance values based on the images, and the actual distancedata is transmitted or transferred to the electrode system 120. Then theelectrode system 120 calculates the respective compensation factors forcalibration.

The catheter 124 is then moved to a second position. Electrical signalsare transmitted between the electrodes 201 and 205 and/or 130 whileimages are taken for the new position. The same methods of calibrationare performed for the second position as was performed for the firstposition. More positions the catheter 124 allow for a bettercalibration. Physical differences between different patients 112 orwithin the same patient 112 may be compensated.

After calibration, capturing images during medical procedures using thecatheter 124 may not be needed. For example, X-ray exposure to thepatient 112 is minimized. Also, during treatment or measurement medicalprocedures, the catheter 124 is moved to a variety of positions by amedical professional, and the reference catheters 128 and/or bodysurface electrodes 130 remain substantially at the same position. Theposition of the catheter 124 during the procedures is determined.

For example, in act 617, an electrical signal is generated between atleast one of the plurality of reference electrodes 205 and/or 130 and atleast one electrode 201. The generation and characteristic of the signalis described above.

In act 621, an electrical characteristic is determined based on thesignal. The electrical characteristic is a blood impedance, any othertissue impedance, such as impedance of lung tissue as well as otherthoracic impedances, a voltage potential, and or any other electricalcharacteristic.

For example, when a current is flowing between one of the electrodes 201and one of the electrodes 205 or 130, an impedance can be calculatedbased on the voltage applied and the actual current value. Thisimpedance is different for different distances between electrodes, andtherefore, the impedance is used to estimate distances betweenelectrodes.

Alternatively, instead of using impedances, voltage potentials betweenelectrodes may be used. For example, when a current is flowing betweenone of the electrodes 201 and one of the electrodes 205 or 130, anelectric field is generated in the same direction as the current. Then avoltage potential, based on the electric field, is measured between twonon-transmitting and/or non-receiving electrodes, such as between anelectrode 201 adjacent to the transmitting and/or receiving electrode201 and an electrode 205 or 130 adjacent to the transmitting and/orreceiving electrode 205 or 130. The voltage potential is different fordifferent distances between electrodes, and, therefore, the voltagepotential is used to estimate distances between electrodes.

In act 625, a position of the catheter 124 is determined based on theelectrical characteristic. For example, estimated distances aredetermined based on the impedance or voltage potential values using atransfer function or any other mathematical technique. Because theposition of the reference electrodes 205 and/or 130 are known, theposition of the electrodes 201 are determined based on the estimateddistances using standard triangulation formulas, trigonometricequations, and/or any other known or future mathematical techniques toderive a three point coordinate position of the electrode 201. Thecorrelated calibration values are used to adjust the estimated distancesto obtain more accurate position data. Because the positions of theelectrodes 201 on the catheter 124 are predetermined, the position ofthe catheter 124 may be determined.

The position data of the catheter 124 is used in conjunction with volumedata or other image data of the patient 112 to create a 3D or virtualimage of the catheter 124 during or after the medical procedure. Forexample, the imaging system 100 or a separate imaging system gathersimage data of an area of the patient 112 associated with the positioningof the catheter 124. The image data may be obtained during or before themedical procedure involving the catheter 124. Based on the image data, a3D image is generated. Any known or future image construction techniquemay be utilized. For example, volume rendering (including voxelarrangement, coordinate transformation, ray casting, and lightingcalculations), surface rendering, image mesh techniques, and/or anyother mathematical or digital signal processing method for generating 3Dimages is used. The position data of the catheter 124 is superimposed orcombined with the 3D image of the internal area of the patient 112 toallow a medical professional view a virtual catheter during or after themedical procedure.

Also, changes in position of internal anatomy based on a heart,breathing, or other physiological cycle may impact the positions of thecatheter 124, the reference catheters 128, and/or the body surfaceelectrodes 130. To limit effects of physiological cycles, the imagingsystem 100, another imaging system, and/or the electrode system 120generates a physiological cycle waveform. The cycle or a portion thereofis used for triggering purposes when electrical characteristicmeasurements between electrodes are acquired. Alternatively, motionartifacts are corrected by creating a 4D motion function of theelectrodes by filming an image sequence, such as an X-ray imagesequence, through one heart beat or respiration cycle. Within eachcycle, each electrode is given a 3D coordinate for each frame by imagesegmentation. The electrodes will then be described by a positionfunction. For example, electrode position=f(x(t), y(t), z(t)), where fis a function in three dimensional space. Once f has been derived, theposition in each X-ray frame is correlated to a certain timestamp duringthe physiological cycle. The timestamp information is synchronized withthe motion of the electrodes, and, therefore, the motion artifacts maybe removed.

Any or all of the data generated by the catheter 124, the referencecatheters 128, the body surface electrodes 130, the imaging system 100,and/or the electrode system 120 is stored in the memory 140 and/or 130.Additionally, instructions executable by the processor 102 and/or 130are stored in a computer-readable medium, such as the memory 106 and/or140. The instructions implement the methods, acts, and processesdescribed above. The instructions for implementing the processes,methods and/or techniques discussed above are provided oncomputer-readable storage media or memories, such as a cache, buffer,RAM, removable media, hard drive or other computer readable storagemedia. Computer readable storage media include various types of volatileand nonvolatile storage media. The functions, acts or tasks illustratedin the figures or described herein are executed in response to one ormore sets of instructions stored in or on computer readable storagemedia. The functions, acts or tasks are independent of the particulartype of instructions set, storage media, processor or processingstrategy and may be performed by software, hardware, integratedcircuits, firmware, micro code and the like, operating alone or incombination. Likewise, processing strategies may includemultiprocessing, multitasking, parallel processing and the like. In oneembodiment, the instructions are stored on a removable media device forreading by local or remote systems. In other embodiments, theinstructions are stored in a remote location for transfer through acomputer network or over telephone lines. In yet other embodiments, theinstructions are stored within a given computer, CPU, GPU or system.Also, any of the features, methods, techniques described may be mixedand matched to create different systems and methodologies.

Any of the features, components, and methods described above may bemixed and matched to provide for a variety of electrode positioningsystems and methodologies. For example, more or less acts may beperformed to accomplish the same end of determining a position of thecatheter 124.

While the invention has been described above by reference to variousembodiments, it should be understood that many changes and modificationscan be made without departing from the scope of the invention. It istherefore intended that the foregoing detailed description be regardedas illustrative rather than limiting, and that it be understood that itis the following claims, including all equivalents, that are intended todefine the spirit and scope of this invention.

1. A system for determining a position of a catheter, the systemcomprising: an electrode on a catheter; a plurality of referenceelectrodes, each of the plurality of reference electrodes configured totransmit or receive a signal to or from the electrode, respectively; anda processor operable to determine a position of the catheter as afunction of an electrical characteristic based on the signals; whereinthe plurality of reference electrodes are not positioned on or in a bodysurface along three mutually orthogonal axes.
 2. The system of claim 1,wherein the signals corresponding to each of the plurality of referenceelectrodes are substantially at a same frequency.
 3. The system of claim1, wherein the electrical characteristic comprises an impedancedetermined by the signal between one of the plurality of referenceelectrodes and the electrode, the impedance used for determining aposition of the electrode.
 4. The system of claim 3, wherein theplurality of reference electrodes comprise body surface electrodes. 5.The system of claim 4, wherein the body surface electrodes compriseelectrocardiogram electrodes.
 6. The system of claim 1, furthercomprising: a first reference catheter, wherein a first set of theplurality of reference electrodes are on the first reference catheter.7. The system of claim 6, further comprising: a second referencecatheter, wherein a second set of the plurality of reference electrodesare on the second reference catheter.
 8. A system for determining aposition of a catheter, the system comprising: first and secondelectrodes on a catheter; a plurality of reference electrodes, each ofthe plurality of reference electrodes configured to transmit or receivea signal to or from the first and second electrodes, respectively; and aprocessor operable to determine a position of the catheter as a functionof a voltage potential between the second electrode and one of theplurality of reference electrodes when the first electrode and anotherone of the plurality of reference electrodes are transmitting andreceiving the signal, respectively.
 9. The system of claim 8, whereinthe voltage potential is based on an electric field generated by thesignal.
 10. The system of claim 8, wherein the first and secondelectrodes are adjacent electrodes.
 11. The system of claim 8, whereinthe plurality of reference electrodes comprise body surface electrodes.12. The system of claim 8, further comprising: a reference catheter,wherein the plurality of reference electrodes are on the referencecatheter.
 13. A method for determining a position of a cathetercomprising: inserting a catheter in a body, the catheter having a firstelectrode; inserting a first reference catheter in the body, the firstreference catheter having a first set of a plurality of referenceelectrodes; generating a signal between one of the plurality ofreference electrodes and the first electrode; determining an electricalcharacteristic based on the signal; and determining a position of thecatheter using the electrical characteristic.
 14. The method of claim13, wherein determining the electrical characteristic comprisesdetermining an impedance based on the signal between one of theplurality of reference electrodes and the first electrode, and whereindetermining the position of the catheter comprises determining aposition of the first electrode using the impedance.
 15. The method ofclaim 14, wherein a second set of the plurality of reference electrodescomprise body surface electrodes.
 16. The method of claim 14, furthercomprising: inserting a second reference catheter in the body, wherein asecond set of the plurality of reference electrodes are on the secondreference catheter.
 17. The method of claim 13, wherein determining theelectrical characteristic comprises determining a voltage potentialbetween one of the plurality of reference electrodes and a secondelectrode on the catheter when the first electrode and another one ofthe plurality of reference electrodes are transmitting and receiving thesignal, respectively, and wherein determining the position of thecatheter comprises determining a position of the second electrode usingthe voltage potential.
 18. The method of claim 17, wherein the voltagepotential is based on an electric field generated by the signal.
 19. Themethod of claim 17, wherein the first and second electrodes are adjacentelectrodes.
 20. The method of claim 13, further comprising: correlatingthe electrical characteristic with a calibration position of thecatheter using an image for viewing the catheter, wherein determiningthe position of the catheter includes using the correlation.